Explaining Entropy responses after a noxious stimulus, with or without neuromuscular blocking agents, by means of the raw electroencephalographic and electromyographic characteristics
ABSTRACT Entropy™, an anaesthetic EEG monitoring method, yields two parameters: State Entropy (SE) and Response Entropy (RE). SE reflects the hypnotic level of the patient. RE covers also the EMG-dominant part of the frequency spectrum, reflecting the upper facial EMG response to noxious stimulation. We studied the EEG, EMG, and Entropy values before and after skin incision, and the effect of rocuronium on Entropy and EMG at skin incision during sevoflurane-nitrous oxide (N₂O) anaesthesia.
Thirty-eight patients were anaesthetized with sevoflurane-N₂O or sevoflurane-N₂O-rocuronium. The biosignal was stored and analysed off-line to detect EEG patterns, EMG, and artifacts. The signal, its power spectrum, SE, RE, and RE-SE values were analysed before and after skin incision. The EEG arousal was classified as β (increase in over 8 Hz activity and decrease in under 4 Hz activity with a typical β pattern) or δ (increase in under 4 Hz activity with the characteristic rhythmic δ pattern and a decrease in over 8 Hz activity).
The EEG arousal appeared in 17 of 19 and 15 of 19 patients (NS), and the EMG arousal in 0 of 19 and 13 of 19 patients (P<0.01) with and without rocuronium, respectively. Both β (n=30) and EMG arousals increased SE and RE. The δ arousal (n=2) decreased both SE and RE. A significant increase in RE-SE values was only seen in patients without rocuronium.
During sevoflurane-N₂O anaesthesia, both EEG and EMG arousals were seen. β and δ arousals had opposite effects on the Entropy values. The EMG arousal was abolished by rocuronium at the train of four level 0/4.
Full-textDOI: · Available from: Antti J Aho, Mar 24, 2015
Acta Anaesthesiologica Scandinavica 08/2013; 57(7). DOI:10.1111/aas.12097 · 2.31 Impact Factor
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ABSTRACT: Although electroencephalogram reactivity (i.e. transient changes in electrical brain activity following external stimulus) might be useful in depth-of-anaesthesia monitoring, it has not been systematically examined with different anaesthetics at doses titrated to unresponsiveness. Three 10-subject groups of healthy volunteers received dexmedetomidine, propofol or sevoflurane in escalating pseudo-steady-state concentrations at 10-min intervals until they did not open their eyes to command. The electroencephalogram was continuously recorded and spectral variables were calculated with short-time Fourier transform and time-varying autoregressive modelling. Electroencephalogram reactivity was most prominent in the midfrontal derivations (termed F3 and F4). During drug-induced unresponsiveness, electroencephalogram reactivity was still present in all drug groups. Dexmedetomidine, propofol and sevoflurane induced distinct suppression patterns on the electroencephalogram reactivity at the same clinical endpoint (unresponsiveness). Reactivity was best maintained with propofol, while only minimally preserved with dexmedetomidine and sevoflurane. Thus, it may be difficult to harness reactivity for depth-of-anaesthesia monitoring.Anaesthesia 09/2014; 70(2). DOI:10.1111/anae.12868 · 3.85 Impact Factor
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ABSTRACT: Dexmedetomidine has been shown to blunt the stress response to surgery. Hence a study was designed to evaluate the effect of intravenous (IV) Dexmedetomidine infusion during general anesthesia for abdominal surgeries on blood glucose levels and on Sevoflurane requirements during anesthesia. Forty patients scheduled for abdominal surgery under general anesthesia were divided into Dexmedetomidine (D) group and Placebo (P) group of 20 each. Group D received a loading dose of Inj. Dexmedetomidine at 1 μg/kg/10 min diluted to 20 mL, followed by maintenance with 0.5 μg/kg/h., till the end of surgery. Group P received similar volume of IV normal saline. Anesthesia was maintained with nitrous oxide in oxygen and Sevoflurane keeping entropy between 40 and 60. Data were analyzed using students t test, chi square test and Fisher Exact test as applicable. During the first postoperative hour, Dexmedetomidine group showed blood glucose levels of 118.2 ± 16.24 mg/dL, compared to placebo group which was 136.95 ± 19.76 mg/dL and it was statistically significant (P < 0.01). Mean hourly Sevoflurane requirement in Group D was 11.10 ± 2.17 mL, compared to 15.45 ± 3.97 mL in placebo group. In peri-operative period, the heart rate and MAP were significantly lower in Group D, when compared to placebo. Patients in Group D were better sedated and post-operative pain score was better in Group D compared to Group P. IV Dexmedetomidine was effective in blunting stress response to surgical trauma as indicated by lower blood glucose levels, and reduces Sevoflurane requirements during entropy guided general anesthesia without affecting time for extubation.Journal of Anaesthesiology Clinical Pharmacology 03/2014; 30(1):25-30. DOI:10.4103/0970-9185.125693